I need to file my late fathers last tax return for 2024. Do I need to set up a new account to use Turbo Tax for that?

Yes.  Online is only good for 1 return and account.  But you can use the same email address for 5 accounts.  You can start another return in TurboTax Online by:

1. Logging out if you are in your account
2. Choose what TurboTax Online product you want to use for the second return
3. Create your account screen
4. Set up a new login for the second return
5. Start working on the new return

The Desktop program can do multiple returns and efile 5 federal for free.